Polyimides are excellent in heat resistance, chemical resistance, mechanical strength, electric properties, etc., and by utilizing these excellent properties, they have been widely used in various technical fields such as aircraft field and electronic field.
As to polyimides for adhesive bonding, heat-resistant adhesive polyimides containing 3,3′-diaminobenzophenone or 1,3-bis(3-aminophenoxy)benzene (abbreviated to APB hereinafter) as a diamine component are disclosed in U.S. Pat. No. 4,065,345 and Japanese Patent Laid-Open Publication No. 143477/1986. Although these polyimides have excellent heat resistance and adhesion properties, they have a problem that their adhesion temperatures need to be set to high temperatures in order to exhibit favorable adhesion.
In Japanese Patent Laid-Open Publication No. 73338/1994 and Japanese Patent Laid-Open Publication No. 322928/1999, polyimides having a siloxane bond or aliphatic units in the polymer as a main chain are disclosed. Although these polyimides have a relatively low glass transition temperature (Tg) advantageous in the adhesion properties, they contain many aliphatic units, whereby not only heat resistance, a feature of polyimide, is lowered but also adhesion properties are deteriorated.